By Michael Maloney
Multishot in-mold assembly, an advanced manufacturing approach that produces multiple, fully assembled components within a single molding process, offers considerable benefits – particularly in liquid silicone rubber (LSR) applications at volumes exceeding 100,000 units.
While the technique demands a higher level of tooling, process and material expertise, its benefits are substantial. Chief among them are reduced product risk, lower total system cost and improved manufacturing reliability.
At its core, multishot in-mold assembly fundamentally changes how products are designed and manufactured. Rather than producing and managing numerous discrete parts that must later be handled, oriented and assembled, components are formed and assembled directly in the mold following highly predictable and repeatable process steps. This dramatically reduces the number of variables—and therefore failure modes—within the finished product.
Reducing Product and Assembly Risk
One of the most significant advantages of multishot in-mold assembly is risk reduction. By eliminating separate part handling and downstream assembly operations, manufacturers reduce the opportunity for misalignment, contamination, damage or assembly error. The number of part-to-part combinations is drastically reduced, which simplifies validation and increases overall process robustness—an especially important consideration in highly regulated industries such as medical devices.
Inventory reduction is another immediate benefit. Managing large volumes of individual molded components introduces cost, complexity and risk, from storage and tracking to reorientation and feeding into assembly workstations. Whether handled manually or through automation, each additional step adds variability. Dedicated assembly automation, while effective, often carries substantial capital expense and long development timelines.
In many cases, part reorientation alone—using bowl feeders, vision systems and auxiliary handling equipment—can exceed $500,000 per part within a subsystem. By contrast, multishot in-mold assembly leverages the inherent orientation created during molding. Eliminating these secondary systems can reduce assembly-related capital and operating costs by 25% or more.
Early Design Collaboration Is Critical
Successful implementation begins long before steel is cut. Early collaboration between product designers, process engineers and brand owners is essential. Many engineering teams naturally approach product development assuming traditional discrete part assembly. Multishot in-mold assembly requires a different mindset—one that considers how parts can be formed, positioned and bonded directly within the tool.
Educating design teams on these capabilities early in the development cycle unlocks opportunities to simplify product architecture, reduce part counts and improve long-term manufacturability.
How Multishot In-Mold Assembly Works
Multishot in-mold assembly can be achieved in several ways. In some applications, a single base material is molded into multiple components within a family mold and assembled upon ejection. In others, multiple shots using different materials—such as thermoplastics combined with elastomers—are injected sequentially or in parallel.
In LSR manufacturing, many products are ultimately assembled onto rigid substrates made of plastic or metal. Multishot tooling allows elastomers to be molded directly onto these substrates, either as functional seals or integrated features.
At the highest level of sophistication, injection pumping systems allow multiple materials—sometimes up to eight distinct shots—to be processed within a single tool. These components can be partially or fully assembled in-mold, or precisely oriented for automated assembly immediately after demolding.
Improved Sealing and Leak Prevention
For sealing applications, multishot in-mold assembly offers a critical functional advantage: leak path elimination. By molding elastomeric seals directly onto one of the mating components, the risk of leakage caused by misplacement or compression variability is significantly reduced. Adhesion between the elastomer and substrate eliminates one potential leak path entirely.
In more complex sealing scenarios, multiple sealing features, such as integrated O-rings. can be molded simultaneously to seal across multiple interfaces. This approach improves sealing reliability while reducing assembly steps and inspection requirements.
Tooling, Automation, Capital Efficiency
Implementing multishot in-mold assembly requires a supplier with deep in-house expertise across tooling, materials, processing and automation. Coordinating these disciplines requires a particular level of aptitude; technical capability within the organization must be significant to ensure reliable execution.
That said, advances in compact mixing, metering and injection systems have reduced the cost and complexity of multishot LSR processing. Compared to scaling traditional injection molding machines for multiple materials, optimized pumping systems allow rubber to be placed precisely within a molding subsystem—improving efficiency and cost control.
Material Considerations
Material selection is central to multishot in-mold assembly success. Whether bonding thermoplastics to thermoplastics or thermoplastics to LSR, adhesion at overmold interfaces must be carefully engineered. In some cases, lower-temperature thermoplastics such as polypropylene or polyethylene are molded as separate but coordinated components, then assembled immediately upon ejection using end-of-arm tooling or compact secondary stations.
Understanding material compatibility, processing temperatures, and adhesion mechanisms ensures long-term product performance and durability.
A Proven First-Mover in Multishot LSR Technology
Silcotech has been a pioneer and first mover in multishot in-mold assembly for liquid silicone rubber since 2001, when the technology was largely absent from North American production manufacturing.
Long before multishot LSR became an industry talking point, Silcotech was executing complex production programs that required the proprietary development of valve-gated cold runner systems, micro-injection tooling and micro-pumping architectures purpose-built for precise material placement and in-mold assembly.
These solutions were developed out of necessity—there was no commercial infrastructure available to support the level of accuracy, repeatability and integration required at the time. The resulting processes—proven in production rather than experimentation—established practical foundations for part orientation, material adhesion and risk reduction that continue to define modern multishot LSR manufacturing.
This depth of experience continues to position Silcotech as a technical leader in advanced silicone molding and integrated in-mold assembly.
Michael Maloney is the cofounder of Silcotech, a North American leader in advanced silicone molding technologies. Based in Bolton, Ontario, Canada, Silcotech specializes in multishot LSR molding, in-mold assembly, and high-complexity manufacturing solutions for medical and industrial applications.
